1. Field of the Invention
The present invention relates to a liquid crystal display, and more particularly to a liquid crystal display for a mobile phone that is adaptive for minimizing horizontal flicker.
2. Description of the Related Art
Generally, liquid crystal displays control the light transmittance of liquid crystals through the use of electric fields, thereby displaying pictures. To this end, the liquid crystal display includes a liquid crystal display panel where liquid crystal cells are arranged in a matrix, and a drive circuit to drive the liquid crystal display panel. Such liquid crystal displays have been commercialized as portable televisions or as display devices of lap-top computers, etc., because they can be made smaller than cathode ray tube (CRT) displays.
Referring to FIG. 1, a mobile phone using a liquid crystal display of the related art includes a liquid crystal display panel 30 and a drive circuit to drive the liquid crystal display panel 30.
The liquid crystal display panel 30 includes liquid crystal cells arranged in a matrix between upper and lower substrates 10 and 20 having thin film transistors (TFT) for switching based on signals supplied to each liquid crystal cell. The thin film transistor is installed at a crossing of gate lines GL and data lines DL for switching data signals in response to scan signals, i.e., gate signals, from the gate line GL, wherein the data signal is to be transmitted to the liquid crystal cell. The liquid crystal display panel 30 is divided into a display part 21 provided with the liquid crystal cells, and a non-display part provided with signal lines for driving the liquid crystal cells.
In the non-display part of the liquid crystal display, there are formed first signal lines 22 formed on one side of the liquid crystal display panel 30 for supplying drive signals to first to (n/2)th gate lines GL, second signal lines 23 formed on the other side of the liquid crystal display panel 30 for supplying drive signals to ((n/2)+1)th to nth gate lines GL, and third signal lines 24 to supply drive signals to the data lines DL.
Further, in the lower part of the non-display part, there are formed first gate pads 32A connected to the first signal lines 22 respectively, data pads 38 connected to the third signal lines 24 respectively, and second gate pads 32B connected to the second signal lines 23 respectively.
A chip-on-film 55 (hereinafter, referred to as COF) is connected to the lower part of the non-display part by a tape-automated-bonding TAB method, wherein the COF has drive circuits mounted thereon to drive the liquid crystal display panel 30. A gate drive integrated circuit 40 for driving the gate lines GL, and a data drive integrated circuit 50 for driving the data lines DL are mounted on the COF 55. On the COF 55, output pads are formed to be connected to the data pads 38 and the first and second gate pads 32A and 32B, and COF signal lines are formed connecting the output pads with the output terminals of the gate drive integrated circuit 40 and the output terminals of the data drive integrated circuit 50, respectively.
The gate drive integrated circuit 40 sequentially supplies scan signals to the gate lines GL in response to control signals from a timing controller, thereby sequentially driving the liquid crystal cells on the liquid crystal display panel 30 by lines. In other words, the gate drive integrated circuit 40 supplies the scan signals to the first to (n/2)th gate lines GL using the first gate signal lines 22 and, in addition, supplies the scan signals to the ((n/2)+1)th to nth gate lines GL using the second gate signal lines 23. In other words, the gate drive integrated circuit 40 supplies the scan signals to flow from left to right in the liquid crystal display panel 30 using the first signal lines 22, and supplies the scan signals to flow from right to left in the liquid crystal display panel 30 using the second signal lines 23.
The data drive integrated circuit 50 supplies pixel voltage signals to each data line DL whenever the scan signal is supplied to any one of the gate lines GL. Accordingly, the liquid crystal display panel 30 controls the light transmittance by the electric field applied between a pixel electrode and a common electrode in accordance with the pixel voltage signal by liquid crystal cells, thereby displaying pictures.
The liquid crystal cells LC on the liquid crystal display panel 30 are driven by a line inversion method in the liquid crystal display for the mobile phone. In a driving method of the liquid crystal display panel, the polarity of the data signals is inverted along the horizontal line, i.e., gate line, on the liquid crystal display panel 30 in the line inversion method.
In the liquid crystal display for the mobile phone driven by the line inversion method, as described above, horizontal flicker are generated due to the polarity difference of the data signals, i.e., the brightness difference and the visual sensation characteristics difference between a positive (+) line and a negative (−) line, because the gate lines GL of the liquid crystal display panel 30 are divided into the first to (n/2)th gate lines GL and the ((n/2)+1)th to nth gate lines GL to be supplied with the scan signals. In other words, the horizontal flickers 80 are generated in the liquid crystal display panel 30, as in FIG. 3, because there occurs a deviation of effective voltage between the common voltage Vcom and the positive (+) and negative (−) voltages of the data signal, as shown in FIG. 2, due to the line resistance of the gate lines GL. Accordingly, picture quality deteriorates due to the foregoing horizontal flickers 80 in the liquid crystal display for the mobile phone of the related art.
In this way, the horizontal flicker generated in the liquid crystal display panel of the liquid crystal display for the mobile phone according to the driving method by the line inversion method are generated when a frame frequency is below 60 Hz, so the horizontal flicker can be improved if the display is driven with the frame frequency above 120 Hz. However, if it is driven with the frame frequency above 120 Hz, there is a disadvantage in that the power consumption of the display increases.
Further, in the liquid crystal display for the mobile phone of the related art, as shown in FIG. 4, the horizontal flickers are generated on the liquid crystal display panel 30 by the capacitance Cpp in accordance with the distance (W) between the liquid crystal cell and the adjacent liquid crystal cells to its top and bottom. In other words, as the capacitance Cpp increases in accordance with the distance (W) between the liquid crystal cells, the voltage difference between horizontal lines also increases, thereby generating the horizontal flickers.
On the other hand, in the liquid crystal display for the mobile phone of the related art, as shown in FIG. 5, the horizontal flickers are generated on the liquid crystal display panel 30 in accordance with the line resistance difference between an input bumper 42 of the gate drive integrated circuit 40 mounted on the COF 55 and the pad of an interface 72 that supplies the drive signal to the gate drive integrated circuit 40.
To be more specific, the drive signal from the pad of the interface 72 is applied to the liquid crystal display panel 30 through the COF 55. In other words, the input bumper 42 of the gate drive integrated circuit 40 is connected to the pad of the interface 72 by a COF signal line 70 on the COF 55. The input bumper 42 of the gate drive integrated circuit 40 receives the drive signal from any one of the pads of the interfaces 72 to drive the gate lines GL. At this moment, as the difference in line resistance of the COF signal line 70 on the COF 55 increases, the voltage difference of the drive signal inputted to the input bumper 42 of the gate drive integrated circuit 40 increases, thereby generating the horizontal flickers due to the polarity difference of the data signals, i.e., the brightness difference and the visual sensation characteristics difference between the positive (+) and negative (−) lines as applied to the liquid crystal cell.